Add an example of request_plus as well

As a developer new to the concept of scan consistency, this page makes me feel like I need to do quite a lot in order to set a scan consistency mode. However it is only necessary to do this for `at_plus`. In fact it is not possible to use at_plus if you insert documents via N1QL INSERT so a simple addition here showing how to set scan consistency to request_plus would be useful. I fell into a trap and lost some time through the following thought process:

Ok I should use at_plus since that is what the example shows. I need a mutation state. How do I get a mutation state? From the last inserted document? Oh...I'm not actually inserting documents via buckets but via N1QL so maybe I need one of the other modes. How do I set the other modes?

Reporter: Jim Borden
E-mail: jim.borden@couchbase.com